Effect of proteolytic activity of Epicoccum purpurascens major allergen, Epi p 1 in allergic inflammation

Airborne indoor allergen serine proteases and their contribution to sensitisation and activation of innate immunity in allergic airway disease

Common airborne allergens (pollen, animal dander and those from fungi and insects) are the main triggers of type I allergic disorder in the respiratory system and are associated with allergic rhinitis, allergic asthma, as well as immunoglobulin E (IgE)-mediated allergic bronchopulmonary aspergillosis. These allergens promote IgE crosslinking, vasodilation, infiltration of inflammatory cells, mucosal barrier dysfunction, extracellular matrix deposition and smooth muscle spasm, which collectively cause remodelling of the airways. Fungus and insect (house dust mite and cockroaches) indoor allergens are particularly rich in proteases. Indeed, more than 40 different types of aeroallergen proteases, which have both IgE-neutralising and tissue-destructive activities, have been documented in the Allergen Nomenclature database. Of all the inhaled protease allergens, 85% are classed as serine protease activities and include trypsin-like, chymotrypsin-like and collagenolytic serine proteases. In this article, we review and compare the allergenicity and proteolytic effect of allergen serine proteases as listed in the Allergen Nomenclature and MEROPS databases and highlight their contribution to allergic sensitisation, disruption of the epithelial barrier and activation of innate immunity in allergic airways disease. The utility of small-molecule inhibitors of allergen serine proteases as a potential treatment strategy for allergic airways disease will also be discussed.

Whole-genome sequencing and functional annotation of pathogenic Paraconiothyrium brasiliense causing human cellulitis

BACKGROUND

A pathogenic filamentous fungus causing eyelid cellulitis was isolated from the secretion from a patient's left eyelid, and a phylogenetic analysis based on the rDNA internal transcribed spacer region (ITS) and single-copy gene families identified the isolated strain as Paraconiothyrium brasiliense. The genus Paraconiothyrium contains the major plant pathogenic fungi, and in our study, P. brasiliense was identified for the first time as causing human infection. To comprehensively analyze the pathogenicity, and proteomics of the isolated strain from a genetic perspective, whole-genome sequencing was performed with the Illumina NovaSeq and Oxford Nanopore Technologies platforms, and a bioinformatics analysis was performed with BLAST against genome sequences in various publicly available databases.

RESULTS

The genome of P. brasiliense GGX 413 is 39.49 Mb in length, with a 51.2% GC content, and encodes 13,057 protein-coding genes and 181 noncoding RNAs. Functional annotation showed that 592 genes encode virulence factors that are involved in human disease, including 61 lethal virulence factors and 30 hypervirulence factors. Fifty-four of these 592 virulence genes are related to carbohydrate-active enzymes, including 46 genes encoding secretory CAZymes, and 119 associated with peptidases, including 70 genes encoding secretory peptidases, and 27 are involved in secondary metabolite synthesis, including four that are associated with terpenoid metabolism.

CONCLUSIONS

This study establishes the genomic resources of P. brasiliense and provides a theoretical basis for future studies of the pathogenic mechanism of its infection of humans, the treatment of the diseases caused, and related research.

Protease allergens as initiators-regulators of allergic inflammation

Tremendous progress in the last few years has been made to explain how seemingly harmless environmental proteins from different origins can induce potent Th2-biased inflammatory responses. Convergent findings have shown the key roles of allergens displaying proteolytic activity in the initiation and progression of the allergic response. Through their propensity to activate IgE-independent inflammatory pathways, certain allergenic proteases are now considered as initiators for sensitization to themselves and to non-protease allergens. The protease allergens degrade junctional proteins of keratinocytes or airway epithelium to facilitate allergen delivery across the epithelial barrier and their subsequent uptake by antigen-presenting cells. Epithelial injuries mediated by these proteases together with their sensing by protease-activated receptors (PARs) elicit potent inflammatory responses resulting in the release of pro-Th2 cytokines (IL-6, IL-25, IL-1β, TSLP) and danger-associated molecular patterns (DAMPs; IL-33, ATP, uric acid). Recently, protease allergens were shown to cleave the protease sensor domain of IL-33 to produce a super-active form of the alarmin. At the same time, proteolytic cleavage of fibrinogen can trigger TLR4 signaling, and cleavage of various cell surface receptors further shape the Th2 polarization. Remarkably, the sensing of protease allergens by nociceptive neurons can represent a primary step in the development of the allergic response. The goal of this review is to highlight the multiple innate immune mechanisms triggered by protease allergens that converge to initiate the allergic response.

Plant-Fungal Interactions: A Case Study of Epicoccoum nigrum Link

Epicoccum nigrum Link is a cosmopolitan species, and it has been described as both an in vitro and in vivo antagonist of many fungal pathogens of plants. However, there are no clear reports about the interactions between E. nigrum and various plant species, and about the effects of culture filtrates produced by this fungus on plants. Therefore, we assessed the interactions between E. nigrum and different plant species, such as sugar beet (Beta vulgaris L. ssp. vulgaris), spring wheat (Triticum aestivum L.), red clover (Trifolium pratense L.), and winter oilseed rape (Brassica napus L.). Additionally, we evaluated the effect of E. nigrum culture filtrates on garden cress (Lepidium sativum L.). Our study showed that the E. nigrum strains varied in terms of the color of excreted culture filtrates and showed different interactions with garden cress. Overall, fungal strains only affected adversely the sprout length in a significant way and, partially, the growth of the tested plant. In addition, we confirmed the suitability of the garden cress as a test plant in in vitro toxicological tests. Most strains of E. nigrum (61.1%) secreted enzymes expected to participate mainly in the later stages of the infection (amylases and proteases) and not those expected to operate in the early phases of host penetration (cellulases and pectinases) that were secreted by 33.3% of fungal strains. The group of pectinolytic enzymes represented the catalysts with the highest activity. Host specialization tests showed that E. nigrum was mainly re-isolated from the plant surface and the number of infected seedlings as well as the disease index depended on a studied plant species, with sugar beet and red clover being most sensitive to infection. In turn, the lowest value of the disease index caused by E. nigrum strains was recorded for spring wheat and winter oilseed rape. Overall, statistically significant differences in the growth of plant seedlings during the host specialization test were noted only for sugar beet and red clover seedlings. The seedlings of plants in the control group (without fungal inoculum) exhibited an increased length compared to those treated with E. nigrum inoculum. Our studies also showed that E. nigrum is probably a facultative saprotroph of plants and it may winter on red clover, which is presumably its main reservoirs, among the species considered.

Aspergillus fumigatus Protease Alkaline Protease 1 (Alp1): A New Therapeutic Target for Fungal Asthma

We review three recent findings that have fundamentally altered our understanding of causative mechanisms underlying fungal-related asthma. These mechanisms may be partially independent of host inflammatory processes but are strongly dependent upon the actions of Alp1 on lung structural cells. They entail (i) bronchial epithelial sensing of Alp1; (ii) Alp1-induced airway smooth muscle (ASM) contraction; (iii) Alp1-induced airflow obstruction. Collectively, these mechanisms point to Alp1 as a new target for intervention in fungal asthma.

Dust mite-derived Der f 3 activates a pro-inflammatory program in airway epithelial cells via PAR-1 and PAR-2

Protease activity of allergens has been suggested to be involved in the pathogenesis of allergic diseases. The major allergen Der f 3 from Dermatophagoides farinae harbors serine protease activity, but its immunopathogenesis remains unclear. This study aims to explore the effect of Der f 3 on the airway epithelial barrier and on the molecular pathways by which Der f 3 induces inflammation. RNA-seq was performed to identify differentially expressed genes in bronchial airway epithelial cells (AEC) between native Der f 3 and heat-inactivated (H) Der f 3, coupled with real-time PCR (RT-PCR) and ELISA for validation. Unlike other protease allergens such as that induce Th2-promoting alarmins (IL-25, IL-33, TSLP) in AECs, Der f 3 induced pro-inflammatory cytokines and chemokines including IL-6, IL-8 and GM-CSF, which are known to promote Th17 response. These pro-inflammatory mediators were induced by Der f 3 via the MAPK and NF-κB pathways as well as the store-operated calcium signaling. Gene silencing with small interfering RNA in A549 and BEAS-2B cells indicated that activation of AECs by Der f 3 was mainly dependent on protease-activated receptor 2 (PAR-2), while PAR-1 was also required for the full activation of AECs. Double knock-down of PAR-1 and PAR-2 largely impaired Der f 3-inducecd IL-8 production and subsequent signaling pathways. Our data suggest that Der f 3 induces pro-inflammatory mediators in human epithelial cell lines via the PARs-MAPK-NF-κB axis. Our results provide a molecular mechanism by which Der f 3 may trigger the Th17-skewed allergic response toward house dust mites.

Spectrum of Allergens and Allergen Biology in India

The growing prevalence of allergy and asthma in India has become a major health concern with symptoms ranging from mild rhinitis to severe asthma and even life-threatening anaphylaxis. The "allergen repertoire" of this subcontinent is highly diverse due to the varied climate, flora, and food habits. The proper identification, purification, and molecular characterization of allergy-eliciting molecules are essential in order to facilitate an accurate diagnosis and to design immunotherapeutic vaccines. Although several reports on prevalent allergens are available, most of these studies were based on preliminary detection and identification of the allergens. Only a few of these allergen molecules have been characterized by recombinant technology and structural biology. The present review first describes the composition, distribution pattern, and natural sources of the predominant allergens in India along with the prevalence of sensitization to these allergens across the country. We go on to present a comprehensive report on the biochemical, immunological, and molecular information on the allergens reported so far from India. The review also covers the studies on allergy- related biosafety assessment of transgenic plants. Finally, we discuss the allergen-specific immunotherapy trials performed in India.

Airway responses towards allergens - from the airway epithelium to T cells

The prevalence of allergic diseases such as allergic rhinitis is increasing, affecting up to 30% of the human population worldwide. Allergic sensitization arises from complex interactions between environmental exposures and genetic susceptibility, resulting in inflammatory T helper 2 (Th2) cell-derived immune responses towards environmental allergens. Emerging evidence now suggests that an epithelial dysfunction, coupled with inherent properties of environmental allergens, can be responsible for the inflammatory responses towards allergens. Several epithelial-derived cytokines, such as thymic stromal lymphopoietin (TSLP), IL-25 and IL-33, influence tissue-resident dendritic cells (DCs) as well as Th2 effector cells. Exposure to environmental allergens does not elicit Th2 inflammatory responses or any clinical symptoms in nonatopic individuals, and recent findings suggest that a nondamaged, healthy epithelium lowers the DCs' ability to induce inflammatory T-cell responses towards allergens. The purpose of this review was to summarize the current knowledge on which signals from the airway epithelium, from first contact with inhaled allergens all the way to the ensuing Th2-cell responses, influence the pathology of allergic diseases.

Taxonomy of Allergenic Fungi

The Kingdom Fungi contains diverse eukaryotic organisms including yeasts, molds, mushrooms, bracket fungi, plant rusts, smuts, and puffballs. Fungi have a complex metabolism that differs from animals and plants. They secrete enzymes into their surroundings and absorb the breakdown products of enzyme action. Some of these enzymes are well-known allergens. The phylogenetic relationships among fungi were unclear until recently because classification was based on the sexual state morphology. Fungi lacking an obvious sexual stage were assigned to the artificial, now-obsolete category, "Deuteromycetes" or "Fungi Imperfecti." During the last 20 years, DNA sequencing has resolved 8 fungal phyla, 3 of which contain most genera associated with important aeroallergens: Zygomycota, Ascomycota, and Basidiomycota. Advances in fungal classification have required name changes for some familiar taxa. Because of regulatory constraints, many fungal allergen extracts retain obsolete names. A major benefit from this reorganization is that specific immunoglobulin E (IgE) levels in individuals sensitized to fungi appear to closely match fungal phylogenetic relationships. This close relationship between molecular fungal systematics and IgE sensitization provides an opportunity to systematically look at cross-reactivity and permits representatives from each taxon to serve as a proxy for IgE to the group.

Per a 10 activates human derived epithelial cell line in a protease dependent manner via PAR-2

BACKGROUND

Protease activity of Per a 10 has been shown to modulate dendritic cells toward Th-2 polarization and to induce airway inflammation.

OBJECTIVE

To elucidate the role of serine protease activity of Per a 10 in inducing biochemical responses in epithelial cells.

METHODS

Per a 10 was inactivated by heat treatment (ΔPer a 10) or AEBSF (iPer a 10). A549 cells were exposed to either enzymatically active/inactive Per a 10. The supernatant was analyzed for the secretion of proinflammatory cytokines by ELISA. Ca(2+) mobilization was analyzed by flow cytometry. A PAR-2 derived synthetic peptide 28GTNRSSKGRSLIGKVDGTSHVTGKGVTC54 was incubated with Per a 10 and the resultant cleaved products were analyzed by LC-MS. PAR-2 activation was inhibited by PAR-2 cleavage inhibiting antibody.

RESULTS

ΔPer a 10 was completely inactivated whereas iPer a 10 showed some residual activity. nPer a 10 having protease activity increased the secretion of IL-6, IL-8 and GMCSF from A549 in a dose and time dependent manner whereas iPer a 10 has reduced cytokine secretion. ΔPer a 10 and rPer a 10 were unable to activate the cells. nPer a 10 mobilized intracellular Ca(2+). nPer a 10 cleaved the PAR-2 derived peptide between arginine and serine residues (36R-S37) to expose PAR-2 ligand SLIGKV, as determined by LC-MS. Incubating with anti-PAR-2 cleavage antibody showed diminished cytokine secretion when treated with nPer a 10.

CONCLUSION

Serine protease activity of Per a 10 activates A549 cells to secrete proinflammatory cytokines by PAR-2 activation and Ca(2+)mobilization and can be exploited therapeutically.

Inhaled allergen bronchoprovocation tests

The allergen bronchoprovocation test is a long-standing exacerbation model of allergic asthma that can induce several clinical and pathophysiologic features of asthma in sensitized subjects. Standardized allergen challenge is primarily a research tool, and when properly conducted by qualified and experienced investigators, it is safe and highly reproducible. In combination with validated airway sampling and sensitive detection techniques, allergen challenge allows the study of several features of the physiology of mainly TH2 cell-driven asthma in relation to the kinetics of the underlying airway pathology occurring during the allergen-induced late response. Furthermore, given the small within-subject variability in allergen-induced airway responses, allergen challenge offers an adequate disease model for the evaluation of new (targeted) controller therapies for asthma in a limited number of subjects. In proof-of-efficacy studies thus far, allergen challenge showed a fair positive predicted value and an excellent negative predictive value for the actual clinical efficacy of new antiasthma therapies, underscoring its important role in early drug development. In this review we provide recommendations on challenge methods, response measurements, sample size, safety, and harmonization for future applications.

The longevity of Th2 humoral response induced by proteases natterins requires the participation of long-lasting innate-like B cells and plasma cells in spleen

The generation of long-lived antibody-secreting cells (ASC) and memory B cells are critical events for an effective vaccine and the choice of adjuvant can influence these processes. Various cellular and molecular mechanism involved in the protease action that determine Th2 responses have been identified. However, direct or indirect actions in the regulation of the induction, survival and longevity of ASC in differential compartments remain largely unknown. We investigated whether the proteolytic activity of proteins are determinant for the modulation of the memory immune response in mice, promoting the differentiation of memory B cells to terminally differentiated end stage cells. Here, we show that the proteolytic activity of Natterins, from the venom of Thalassophryne nattereri Brazilian fish, besides inducing a Th2 response with plasmatic titers of high-affinity antigen-specific IgE over extended periods is sufficient for the generation of signals that contribute to the formation of a survival niche in the spleen, essential for the longevity of the main subtype of ASC with B220^neg phenotype.

Serine protease inhibitor attenuates ovalbumin induced inflammation in mouse model of allergic airway disease

Background

Serine proteases promote inflammation and tissue remodeling by activating proteinase-activated receptors, urokinase, metalloproteinases and angiotensin. In the present study, 4-(2-Aminoethyl) benzenesulfonyl fluoride (AEBSF) a serine protease inhibitor was evaluated for prophylactic and therapeutic treatment in mouse model of airway allergy.

Methods

BALB/c mice were sensitized by i.p route and challenged with ovalbumin. They were treated i.n. with 2, 10 and 50 µg of AEBSF, one hour before or after challenge and euthanized to collect BALF (bronchoalveolar lavage fluid), blood and lungs. Proteolytic activity, total cell/eosinophil/neutrophil count eosinophil peroxidase activity (EPO), IL-4, IL-5, IL-10, IL-13, cysteinyl leukotrienes and 8-isoprostane were determined in BALF and immunoglobulins were measured in serum. H&E and PAS stained lung sections were examined for cellular infiltration and airway inflammation.

Results

Mice exposed to ovalbumin and treated with PBS showed increased cellular infiltration in lungs and higher serum IgE, IgG1 and IgG2a levels as compared to sham mice. Treatment with AEBSF reduced total cells/eosinophil/neutrophil infiltration. Both prophylactic and therapeutic AEBSF treatment of 10 or 50 µg reduced serum IgE and IgG1 significantly (p<0.05) than control. AEBSF treatment reduced the proteolytic activity in BALF. IL-4 IL-5 and IL-13 levels decreased significantly (p<0.05) after AEBSF treatment while IL-10 levels increased significantly (p<0.05) in BALF. Airway inflammation and goblet cell hyperplasia reduced as demonstrated by lung histopathology, EPO activity and cysteinyl leukotrienes in BALF after treatment. AEBSF treatment also suppressed oxidative stress in terms of 8-isoprostane in BALF. Among the treatment doses, 10 or 50 µg of AEBSF were most effective in reducing the inflammatory parameters.

Conclusions

Prophylactic and therapeutic treatment with serine protease inhibitor attenuates the airway inflammation in mouse model of airway allergy and have potential for adjunct therapy.

Serine protease Per a 10 from Periplaneta americana bias dendritic cells towards type 2 by upregulating CD86 and low IL-12 secretions

BACKGROUND

Serine protease activity of Per a 10 from Periplaneta americana induces airway inflammation and systemic Th2 response towards self and bystander allergen.

OBJECTIVE

In the present study the effect of proteolytic activity of Per a 10 allergen on dendritic cells (DCs) polarization and consequent T cell response was investigated.

METHODS

Non-atopic subjects with no family history of asthma/allergy were recruited for the study. CD14(+) peripheral blood monocytes were purified, differentiated to immature DCs and stimulated with proteolytically active/inactivated native or recombinant Per a 10. DCs phenotype was analysed with flow cytometry and antigen presenting function assessed by co-culturing with autologous CD4(+) T cells. Cytokine levels were determined using ELISA.

RESULTS

Immature DCs differentiated into mature CD14(-)CD83(+)HLA-DR(+) cells after incubating with proteolytically active/inactivated or recombinant Per a 10. Proteolytically active Per a 10 induced significant CD86 up-regulation on DCs compared to inactivated or recombinant Per a 10 lacking enzymatic activity. Proteolytic activity of Per a 10 showed dose-dependent effect on expression of CD80, CD86, CD83, CD1a and HLA-DR. However, no significant differences were observed phenotypically in active or inactive forms except for CD86. Active Per a 10 stimulated DCs secreted significantly low IL-12 (P < 0.01) and high IL-6, compared to inactive forms of Per a 10. Naive CD4(+) T cells primed with active Per a 10 pulsed DCs also secreted significantly less IL-12 (P < 0.01) and high IL-4, IL-5 plus IL-6 (P < 0.01); in contrast to DCs pulsed with inactivated or recombinant Per a 10.

CONCLUSION AND CLINICAL RELEVANCE

Proteolytic activity of Per a 10 modulates DCs towards type 2 by CD86 up-regulation, high IL-6 and reduced IL-12 secretions. Proteolytically inactive Per a 10 can be further explored for immunotherapy.

A contaminant trypsin-like activity from the timothy grass pollen is responsible for the conflicting enzymatic behavior of the major allergen Phl p 1

We intend to solve whether or not Phl p 1 can be regarded as a protease. A group reported that Phl p 1 has papain-like properties and later on, that this allergen resembles cathepsin B, while another one demonstrated that Phl p 1 lacks proteinase activity and suggested that the measured activity may rise either from a recombinant Phl p 1 contaminant or as a result of an incompletely purified natural allergen. A third group reported Phl p 1 to act by a non-proteolytic activity mechanism. We report the purification of the natural Phl p 1 by means of hydrophobic interaction, gel filtration and STI-Sepharose affinity chromatographies. The Phl p 1 purity was assessed by silver-stained SDS-PAGE and by 'in-gel' and 'gel-free' approaches associated to mass spectrometry analyses. The proteolytic activity was measured using Boc-Gln-Ala-Arg-AMC and Z-Phe-Arg-AMC as substrates. While amidolytic activity could be measured with Phl p 1 after rechromatography on gel filtration, it however completely disappeared after chromatography on STI-Sepharose. The contaminant activity co-eluting with Phl p 1 was not affected by cysteine proteases inhibitors and other thiol-blocking agents, by metalloproteases inhibitors and by aspartic proteases inhibitors. However, it was completely inhibited by low molecular weight and proteinaceous serine proteases inhibitors. TLCK, but not TPCK, inhibited the contaminant activity, showing a trypsin-like behavior. The pH and temperature optimum were 8.0 and 37°C, respectively. These data indicated that Phl p 1 is not a protease. The contaminant trypsin-like activity should be considered when Phl p 1 allergenicity is emphasized.

Role of Allergen Source-Derived Proteases in Sensitization via Airway Epithelial Cells

Protease activity is a characteristic common to many allergens. Allergen source-derived proteases interact with lung epithelial cells, which are now thought to play vital roles in both innate and adaptive immune responses. Allergen source-derived proteases act on airway epithelial cells to induce disruption of the tight junctions between epithelial cells, activation of protease-activated receptor-2, and the production of thymic stromal lymphopoietin. These facilitate allergen delivery across epithelial layers and enhance allergenicity or directly activate the immune system through a nonallergic mechanism. Furthermore, they cleave regulatory cell surface molecules involved in allergic reactions. Thus, allergen source-derived proteases are a potentially critical factor in the development of allergic sensitization and appear to be strongly associated with heightened allergenicity.

Protease-activated receptor 2 activation of myeloid dendritic cells regulates allergic airway inflammation

Background

A common characteristic of allergens is that they contain proteases that can activate protease-activated receptor (PAR-2); however the mechanism by which PAR-2 regulates allergic airway inflammation is unclear.

Methods

Mice (wild type and PAR-2-deficient) were sensitized using German cockroach (GC) feces (frass), the isolated protease from GC frass, or through adoptive transfer of GC frass-treated bone marrow-derived dendritic cells (BMDC) and measurements of airway inflammation (cellular infiltration, cytokine expression, and mucin production), serum IgE levels and airway hyperresponsiveness (AHR) were assessed. BMDC were cultured, treated with GC frass and assessed for cytokine production. PAR-2 expression on pulmonary mDCs was determined by flow cytometry.

Results

Exposure to GC frass induced AHR and airway inflammation in wild type mice; however PAR-2-deficient mice had significantly attenuated responses. To directly investigate the role of the protease, we isolated the protease from GC frass and administered the endotoxin-free protease into the airways of mice in the presence of OVA. GC frass proteases were sufficient to promote the development of AHR, serum IgE, and Th2 cytokine production. PAR-2 expression on mDC was upregulated following GC frass exposure, but the presence of a functional PAR-2 did not alter antigen uptake. To determine if PAR-2 activation led to differential cytokine production, we cultured BMDC in the presence of GM-CSF and treated these cells ex vivo with GC frass. PAR-2-deficient BMDC released significantly less IL-6, IL-23 and TNFα compared to BMDC from wild type mice, suggesting PAR-2 activation was important in Th2/Th17 skewing cytokine production. To determine the role for PAR-2 on mDCs on the initiation of allergic airway inflammation, BMDCs from wild type and PAR-2-deficient mice were treated in the presence or absence of GC frass and then adoptively transferred into the airway of wild type mice. Importantly, GC frass-stimulated wild type BMDCs were sufficient to induce AHR and allergic airway inflammation, while GC frass-stimulated PAR-2-deficient BMDC had attenuated responses.

Conclusions

Together these data suggest an important role for allergen activation of PAR-2 on mDCs in mediating Th2/Th17 cytokine production and allergic airway responses.

Fungal proteases and their pathophysiological effects

Proteolytic enzymes play an important role in fungal physiology and development. External digestion of protein substrates by secreted proteases is required for survival and growth of both saprophytic and pathogenic species. Extracellular serine, aspartic, and metalloproteases are considered virulence factors of many pathogenic species. New findings focus on novel membrane-associated proteases such as yapsins and ADAMs and their role in pathology. Proteases from fungi induce inflammatory responses by altering the permeability of epithelial barrier and by induction of proinflammatory cytokines through protease-activated receptors. Many fungal allergens possess proteolytic activity that appears to be essential in eliciting Th2 responses. Allergenic fungal proteases can act as adjuvants, potentiating responses to other allergens. Proteolytic enzymes from fungi contribute to inflammation through interactions with the kinin system as well as the coagulation and fibrinolytic cascades. Their effect on the host protease-antiprotease balance results from activation of endogenous proteases and degradation of protease inhibitors. Recent studies of the role of fungi in human health point to the growing importance of proteases not only as pathogenic agents in fungal infections but also in asthma, allergy, and damp building related illnesses. Proteolytic enzymes from fungi are widely used in biotechnology, mainly in food, leather, and detergent industries, in ecological bioremediation processes and to produce therapeutic peptides. The involvement of fungal proteases in diverse pathological mechanisms makes them potential targets of therapeutic intervention and candidates for biomarkers of disease and exposure.

Seeking common pathophysiology in asthma, atopy and sinusitis

Asthma and chronic sinusitis are inexplicably common airway diseases that are linked to atopy and allergic inflammation. T helper type 2 (Th2) cells and the associated cytokines are believed to play crucial pathogenic roles in asthma, but the environmental factors that instigate allergic airway disease remain poorly understood. Environmental proteinases are highly allergenic and are candidate inducers of airway Th2 responses. Determining the proteinases and their sources that are relevant to airway disease, however, remains challenging. In this Opinion, we summarize the evidence that implicates fungi as both a relevant source of allergenic proteinases and a potential cause of asthma, atopy and chronic sinusitis through airway infection. Clarification of the extrinsic causes of these processes will markedly improve diagnosis, prognosis and therapy.

German cockroach frass proteases modulate the innate immune response via activation of protease-activated receptor-2

Allergen exposure can induce an early innate immune response; however, the mechanism by which this occurs has not been addressed. In this report, we demonstrate a role for the active serine proteases in German cockroach (GC) feces (frass) and protease-activated receptor (PAR)-2 in modulating the innate immune response. A single exposure of GC frass induced inflammatory cytokine production and cellular infiltration in the airways of mice. In comparison, exposure to protease-depleted GC frass resulted in diminution of inflammatory cytokine production and airway neutrophilia, but had no effect on macrophage infiltration. Selective activation of PAR-2 confirmed that PAR-2 was sufficient to induce airway inflammation. Exposure of GC frass to PAR-2-deficient mice led to decreased immune responses to GC frass compared to wild-type mice. Using the macrophage as an early marker of the innate immune response, we found that GC frass induced significant release of tumor necrosis factor-alpha from primary alveolar macrophages. This effect was dependent on the intrinsic proteases in GC frass. We confirmed GC frass-induced cytokine expression was mediated by activation of NF-kappaB and ERK in a macrophage cell line. Collectively, these data suggest a central role for GC frass protease-PAR-2 activation in regulating the innate immune response through the activation of alveolar macrophages. Understanding the potential role of protease-PAR-2 activation as a danger signal or adjuvant could yield attractive therapeutic targets.

Mucosal sensitization to German cockroach involves protease-activated receptor-2

BACKGROUND

Allergic asthma is on the rise in developed countries. A common characteristic of allergens is that they contain intrinsic protease activity, and many have been shown to activate protease-activated receptor (PAR)-2 in vitro. The role for PAR-2 in mediating allergic airway inflammation has not been assessed using a real world allergen.

METHODS

Mice (wild type or PAR-2-deficient) were sensitized to German cockroach (GC) feces (frass) or protease-depleted GC frass by either mucosal exposure or intraperitoneal injection and measurements of airway inflammation (IL-5, IL-13, IL-17A, and IFNgamma levels in the lung, serum IgE levels, cellular infiltration, mucin production) and airway hyperresponsiveness were performed.

RESULTS

Following systemic sensitization, GC frass increased airway hyperresponsiveness, Th2 cytokine release, serum IgE levels, cellular infiltration and mucin production in wild type mice. Interestingly, PAR-2-deficient mice had similar responses as wild type mice. Since these data were in direct contrast to our finding that mucosal sensitization with GC frass proteases regulated airway hyperresponsiveness and mucin production in BALB/c mice (Page et. al. 2007 Resp Res 8:91), we backcrossed the PAR-2-deficient mice into the BALB/c strain. Sensitization to GC frass could now occur via the more physiologically relevant method of intratracheal inhalation. PAR-2-deficient mice had significantly reduced airway hyperresponsiveness, Th2 and Th17 cytokine release, serum IgE levels, and cellular infiltration compared to wild type mice when sensitization to GC frass occurred through the mucosa. To confirm the importance of mucosal exposure, mice were systemically sensitized to GC frass or protease-depleted GC frass via intraperitoneal injection. We found that removal of proteases from GC frass had no effect on airway inflammation when administered systemically.

CONCLUSIONS

We showed for the first time that allergen-derived proteases in GC frass elicit allergic airway inflammation via PAR-2, but only when allergen was administered through the mucosa. Importantly, our data suggest the importance of resident airway cells in the initiation of allergic airway disease, and could make allergen-derived proteases attractive therapeutic targets.

New insights into innate immune mechanisms underlying allergenicity

Allergic diseases, which have reached epidemic proportions, are caused by inappropriate immune responses to a relatively small number of environmental proteins. The molecular basis for the propensity of specific proteins to promote maladaptive, allergic responses has been difficult to define. Recent data suggest that the ability of such proteins to promote allergic responses in susceptible hosts is a function of their ability to interact with diverse pathways of innate immune recognition and activation at mucosal surfaces. This review highlights recent insights into innate immune activation by allergens--through proteolytic activity, engagement of pattern recognition receptors, molecular mimicry of TLR signaling complex molecules, lipid-binding activity, and oxidant potential--and the role of such activation in inducing allergic disease. A greater understanding of the fundamental origins of allergenicity should help define new preventive and therapeutic targets in allergic disease.

Purification and immunological characterization of a 12-kDa allergen from Epicoccum purpurascens

Exposure to Epicoccum purpurascens is implicated in respiratory allergies and asthma. Several allergens of clinical importance were identified in Epicoccum extract (EE), but only one allergen has been isolated and characterized. In the present study, a 12-kDa allergen was isolated from an Epicoccum spore-mycelial extract by concanavalin-A sepharose, reverse-phase hydrophobic and gel filtration chromatography. The purified protein was recognized as a single 12-kDa allergen on immunoblot with a serum pool of Epicoccum-sensitive patients. Of the 94 respiratory allergy patients tested intradermally, 17 showed marked positive skin reactions to EE and 12 of them reacted with the 12-kDa protein, indicating a diagnostic sensitivity of 70%. More than 80% patients' sera showed immunoglobulin E (IgE) reactivity to the purified protein in enzyme-linked immunosorbent assay and immunoblot, identifying it as a major allergen. Preincubation of pooled serum with the protein led to inhibition of IgE binding to solid-phase-bound EE (effective concentration 50%=180 ng). Twelve of the 17 serum samples showed significant basophil histamine release upon stimulation with purified protein. The protein induced significant proliferation of peripheral blood mononuclear cells of 13 patients. A high level of interleukin-4 in the culture supernatant of these cells indicated induction of a T-helper type 2 response. The purified 12-kDa protein is a clinically relevant allergen and has potential for the diagnosis and therapy of Epicoccum allergies.